The invention relates generally to electrical enclosures such as battery chargers, power centers, rectifiers and transformers used in dusty, low headroom environments such as in underground mines. In particular, it relates to improved ventilating and cooling apparatus for same.
A "power center" used in underground coal mines is one example of an electrical enclosure where the present invention is useful. It has an elongated housing often mounted on skids for movement about an underground coal mine. It receives electrical energy at high voltage, up to 15,000 volts and has a number of transformers and other internal components which produce lower voltage outputs. For example, it may have alternating current input at 15,000 volts and outputs at various lower voltages in direct and alternating current configurations. There may be one or more output circuits providing, say, 1500 volts for a continuous miner, 220 or 420 volts for conveyor drive motors, and 110 volts AC or DC for underground lighting circuits.
These are principally mobile transformer stations including one or more power transformers and associated high low voltage circuit breakers together with various protective devices and instrumentation.
Power centers for longwall mining systems tend to increase in capacity from year to year. A typical, modern power center may have over 2,000,000 watts of transformer capacity producing up to 30,000 watts of heat loss which must be dissipated from the enclosure. Attempts to dissipate heat of this magnitude by simple convection and radiation devices are unsatisfactory and result in the internal components becoming overheated.
The problem is exacerbated by the overall shape of typical power centers used in United States coal mining practice where mine entries and rooms are little higher than the thickness of the coal seam and the top wall is often so close to the roof that no effective internal or external convection cooling up drafts can be developed. Dimensions of a typical longwall power center may be 20 feet long, 6 feet wide, and 3 feet high.
Transformers used in these low-height enclosures are often of a special design to suit the height restriction, but even so, the top of the transformer core comes to within 2 to 3 inches of the top wall. The top wall itself must be imperforate, having no ventilation holes through which dust and roof debris can enter the enclosure.
Another problem exacerbating cooling of the internal components by convection air currents, in addition to the above-mentioned proximity of the top wall to the roof, is the great number of switches, meters, and electrical connectors commonly provided in the side walls leaving little room for ventilation louvers.
As a result of the circumstances described above, convection is no longer effective to dissipate the heat developed in modern high-capacity electrical enclosures. A stagnant layer of very hot air accumulates inside the enclosure just below the top wall. Without ventilation augmentation provided by the present invention, this can shorten the life of the electrical components, causing them to fail prematurely.